1. Field of the Invention
The present invention relates to an apparatus detecting motion in an input video frame (i.e., a single image in a sequence of images) and a detecting method thereof, and more particularly, to an apparatus detecting motion of image data by using a compressed encoded bit stream and a detecting method thereof.
2. Description of the Related Art
The demand for an automatic monitoring system has been recently increased, and a network image monitoring system using a computer or Internet is being developed. Following the trend of the time, digitalization of the existing analog monitoring systems is also being actively developed. The digital monitoring systems can prevent stored images from being damaged. Moreover, a network digital image monitoring system allows easy search and process of a desired digital data, and has various usages and advantages due to easy monitoring using the network.
The amount of image data input into the digital monitoring system can be very vast/large. Therefore, an image compression technology is required to transmit or store the data. For the image compression technology, mainly overlapping elements in an area or a time domain are removed. Besides compressing the image data, a method of transmitting an image data in which a motion is detected to a distant operator, a PDA set up in advance, or an IMT terminal or a method of storing the image into an FTP server is used. When the above methods are applied, the monitoring system can be effectively operated without unnecessarily loading the system because of the large amount of data. Furthermore, when only the image having a motion is stored into a hard disk, in case of a Digital Video Recorder (DVR), the efficiency of the hard disk can be improved. Thus, when the DVR product or the network monitoring system involves a function of motion detection, the efficiency of the product is improved and the added value of the product is also increased.
As a conventional method of detecting the motion from the input image, a method of detecting the motion based on a pixel value of a difference image gained/calculated by obtaining the difference between a previous image and a current image is used. In other words, a statistic featuring value, such as an average and a standard deviation, is derived from the pixel value gained from the difference image, and the statistic featuring value is compared with a threshold gained through an experiment so that the motion can be detected from the image.
FIG. 1 is a block diagram showing a conventional apparatus for detecting motion in an input image using the difference image technique, and FIG. 2 is a flow chart showing a method of detecting the motion using the detecting apparatus shown in FIG. 1. As shown in FIG. 1, the conventional motion detecting apparatus comprises an A/D conversion unit 10, a filtering unit 20, a memory 30, an operation unit 40, a comparison unit 50 and a warning unit 60. In FIG. 2, the method of detecting the motion in the apparatus having the above structure is as follows. Initially, the A/D conversion unit 10 converts an analog signal of the image, input through a camera, into a digital signal. Noise is removed from the converted digital image data at the noise removing filtering unit 20, and then the noise-free converted digital image data is input into the memory 30 and the operation unit 40. At operations 10 and 20, the memory 30 stores a previously input image (P) and a currently input image (C) to compare the images, and, at operation 30, the operation unit 40 obtains a difference image (D) of the noise free currently input image (C) and the previously input image (P) stored in the memory 30. Moreover, at operation 40, the comparison unit 50 compares the difference image (D) value of each pixel with a threshold (t1) to determine which pixel has a motion, and, at operations 41 and 42, a motion binarization process generates a binarized motion image by converting each pixel to a pixel having the motion or without the motion (i.e., a binarization of the difference image based upon classification of each pixel as a motion pixel or a without-motion pixel based upon the threshold motion classification in operation 40). Then, at operation 50, the operation unit 40 calculates the entire sum (ΣBD) of the pixels converted to binarized image (BD). At operation 60, the sum (ΣBD) of the entire pixels of the binarized image (BD) is compared with a predetermined threshold (t2). At operation 60, if the sum (ΣBD) of the binarized image (BD) is greater than the threshold (t2), it is judged that there has been motion in the currently input image (C) and at operation 70, a motion detection warning is generated from the warning unit 60.
The motion detecting method using the difference image can obtain a great amount of information from each pixel unit, and has an advantage of detecting a motion by using various statistical features of the difference image. However, the operation of the conventional motion detecting method is slow because data is obtained/processed for each pixel unit, and there is a disadvantage that the detected result can be sensitive to/negatively impacted by camera noise or a change of the external environment.
Moreover, the method of detecting the motion in an input image by using the difference image requires extra frame memory to store the previous and current input image data to compare the previously input image and the currently input image. Such a method also requires a noise-removing filter to prevent mis-operation caused by the camera noise. Furthermore, it is difficult to set up the thresholds (t1) and (t2) to judge/detect whether an image has a motion.